An orbital sander achieves an eccentric sanding motion through linkage of its motor to a sanding platen via an off-axis bearing. In conventional orbital sanders, an eccentric member is fixed to the drive shaft of the motor, thereby defining a single eccentric orbit. Depending on the nature of this orbit, such a sander is suitable either specifically for coarse sanding work or for fine sanding work.
Various attempts have been made to provide a sander capable of performing both coarse and fine sanding tasks. For example, U.S. Pat. No. 3,364,625 to Sogge and U.S. Pat. No. 5,357,715 to Hiramatsu disclose sanders capable of operating in an orbital mode as a well as a stationary mode. Through gearing or reversal of the direction of motor rotation, these sanders permit the use of an orbital motion for fine sanding work and a stationary rotation of the sanding platen for faster stock removal. Alternatively, U.S. Pat. No. 3,874,125 to Stroezel discloses a sander capable of converting from an orbital motion to a reciprocatory motion in response to a reversal in the direction of motor rotation.
Using a different approach, U.S. Pat. No. 4,744,177 to Braun et al. discloses an orbital sander in which the direction of motor rotation determines which of two different eccentric orbits of the sanding platen is selected. Although this sander allows for both coarse and fine sanding work while still maintaining the benefit of an orbital motion, the sander is configured such that the eccentric mechanism substantially increases the overall height of the sander, thereby hindering its operability. Furthermore, the eccentric member is supported by elastic elements between the platen and sander housing, precluding use of the sander in a random orbital mode.